1. Field of the Invention
The present invention relates to a surgical instrument used to seize or cut tissue, for example, in an endoscopic surgical operation in the body cavity, such as laparoscopic surgery or surgery.
2. Description of the Related Art
Conventional forceps used to seize or cut tissue in an endoscopic surgical operation are described in Jpn. Pat. Appln. KOKAI Publication No. 4-246344 and EPO No. 484,671 A2. In these forceps, an openable forceps section is attached to the distal end of a body section having an outer tube and an operating section mounted on the proximal end of the outer tube. The outer tube is penetrated by a rod member. The forceps section is opened or closed by operating the operating section to move the rod member.
The forceps section is composed of a pair of forceps members which are rockable around a pivot pin, and a straight cam groove is formed in the rear end portion of each forceps member. Engaging pins, which are adapted to engage their corresponding cam grooves simultaneously, protrude from the distal end portion of the operating rod member. As the engaging pins move in association with the movement of the rod member, the forceps members swing around the pivot pin.
In a forceps for surgical operation described in West German Gebrauchsmuster (Utility Model) No. G8809501, a pair of forceps members rockable around a pivot pin and a movable guide member are attached to the distal end portion of a rod-shaped forceps body. An extension portion is provided on the rear end portion of each forceps member. The guide member is provided with guide channels in which the extension portions are inserted individually. The guide channels are formed as through holes which open on the distal end face and side face of the guide member. As the guide member is moved by means of the operating rod member, the extension portions of the forceps members are inserted into their corresponding guide channels to change the state of engagement, whereby the forceps members are opened or closed.
According to these forceps, however, when the forceps members are urged to open wide to cut tissue or seize an instrument or tissue, the rear end portions of the members inevitably project long beyond the diameter of the outer tube of an insertion section as the forceps body.
Each forceps of this type is passed through a cylindrical trocar when it is used. If you try to draw out the forceps with the rear end portions of the forceps members projecting from the body, therefore, the members are caught by the front end of the trocar, and cannot be easily closed. In delivering a suture into the body cavity in a manner such that it is twined around the outer tube, moreover, the suture is liable to be caught by the rear end portions of the forceps members projecting from the tube.
According to the latter forceps, the extension portions of the forceps members project long beyond the diameter of the insertion section through the guide channels when the forceps members are opened. Besides being subject to the aforesaid drawback, therefore, the forceps can be easily broken owing to the slenderness of their extension portions when the forceps section is left open, the extension portions project diagonally rearward. In this state, therefore, the extension portions may possibly be caught by the front end of the trocar, so that the forceps cannot be removed at once.
As an open-close mechanism for the forceps section, on the other hand, a four-joint parallel link mechanism may be arranged such that its two links are formed of the respective proximal end portions of the forceps members when the forceps members are opened wide, in this arrangement, however, the links project long beyond the diameter of the outer tube of the insertion section. With the forceps members left open in this manner, the forceps cannot be drawn out of the trocar. As is the case with the four-joint link mechanism, the force applied at the distal end portion is smallest when the forceps members are fully closed. Functionally, therefore, the mechanism of this type has a disadvantage that if its links are small in size, then the forceps' capability of seizing or cutting tissue is low. It is not advisable, therefore, to diminish the projection of the links by reducing the size of the links of the link mechanism. Thus, the links inevitably project long beyond the diameter of the outer tube of the insertion section when the forceps members are opened wide.
In cauterizing tissue in the body cavity by means of high-frequency current with use of the operative forceps of this type as a probe, moreover, there is a possibility of the projecting portions of the open-close mechanism touching and unexpectedly cauterizing some other regions outside a target region. Accordingly, an operator is expected to perform an operation carefully with a high technique.
Furthermore, some portions of the open-close mechanism for the forceps members project outside the diameter of the outer tube of the insertion section, and are bound to be exposed. In some cases, therefore, blood or other body fluids may get into the open-close mechanism, thereby hindering the open-close operation.